1. Technical Field
The present invention relates to a sheet reversing apparatus, an image forming apparatus, and a sheet reversing method.
2. Background Technology
A sheet handling apparatus, such as an image forming apparatus, conveys the sheet in the apparatus, performs an image formation and the like, and further conveys the sheet performed with the image formation in the apparatus. In the case of conveying the sheet, in order to improve the conveyance efficiency, the sheet handling apparatus generally conveys the sheet with lateral feeding by setting a long edge of the sheet at the leading edge of the conveyance direction. However, in cases where the size in long edge of the sheet becomes large, the conveyance becomes difficult due to size restriction in the apparatus, therefore, for the sheet of larger size than a prescribed size, the sheet conveyance with longitudinal feeding, by setting the short edge of the sheet at the leading edge of the conveyance direction, is required.
In the meantime, in case of feeding the sheet in the apparatus, if a skew or misalignment of the sheet arises, images may not properly formed on the sheet, sheet jams may arise, and proper processing may become difficult in a post-processing after the image formation. Therefore, means for detecting the sheet position or sheet skew and connecting the skew or the misalignment of sheet are conventionally implemented (please refer to Patent document 1: JPA2008-230733 and Patent document 2: JPA2010-64820).
Skew correction mechanisms of the sheet will be described referring to rough example drawings of FIGS. 9a and 9b. In FIG. 9a, at the downstream side of front/back reversing conveyance section 60, which is provided with a reversing mechanism for front/hack sides reversing of sheet P, two independent guide rollers 61a and 61b are arranged along a perpendicular direction to the conveyance direction of sheet P, and said guide rollers 61a and 61b are independently driven by correction motors 62a and 62b, which enables the conveyance of sheet P. Further, near in the downstream of the guide rollers 61a and 61b, sheet skew detection sensors 63a and 63b are arranged, on a sheet conveyance path, along a perpendicular direction to the conveyance direction of sheet P, which detect the leading of sheet P being conveyed.
In this skew correction mechanism, sheet skew detection sensor 63a and 63b detect the leading edge of sheet P conveyed on the sheet conveyance path by guide rollers 61a and 61b which rotate at a constant speed. As the result of detection, if a difference of detection times is not detected between detection sensors 63a and 63b, sheet skew is determined to be not existing, and if the difference is detected, sheet skew is determined to be existing. In cases where the sheet skew is existing, by adjusting the rotation speeds of sheet skew correction motors 62a and 62b based on the above detection result, the correction mechanism sets a difference between the rotation speeds in conveyance direction of guide rollers 61a and 61b to correct the sheet skew and convey the sheet P. In cases where the sheet skew does not exist, the correction mechanism rotates guide rollers 61a and 61b in a constant speed by sheet skew correction motors 62a and 62 to convey the sheet P.
In FIG. 9b, at the downstream side of front/back reversing conveyance section 65, two guide rollers 66a and 66b are arranged along a perpendicular direction to the conveyance direction of sheet P, and said guide rollers 66a and 66b are mounted on a common drive shaft 67 to convey sheet P. Drive shat 67 is driven by sheet skew correction motor 68. Sheet skew correction motor 68 enables a change of conveyance direction by drive shaft 67, through rotating drive shaft 67 by a prescribed amount in a surface direction of the sheet.
Further, near in the downstream of the guide rollers 66a and 66b, sheet skew detection sensors 69a and 69b are arranged, on a sheet conveyance path, along a perpendicular direction to the conveyance direction of sheet P, which detect the leading of sheet P being conveyed.
In this skew correction mechanism, sheet skew detection sensor 69a and 69b detect the leading edge of sheet P. As the result of detection, if a difference of detection times is not detected between detection sensors 69a and 69b, sheet skew is determined to be not existing, and if the difference is detected, sheet skew is determined to be existing. In cases where the sheet skew is existing, by adjusting the angle of drive shaft 67 in the sheet surface direction by sheet skew correction motor 68 based on the above detection result, the correction mechanism rotates guide rollers 66a and 66b rotatably mounted on drive shaft 67 by sheet skew correction motor 68 at a constant speed, and to convey the sheet P by correcting the sheet skew. In cases where the sheet skew does not exist, the correction mechanism positions drive shaft 67 along the direction perpendicular to the sheet conveyance direction, and rotates guide rollers 61a and 66b in a constant speed by sheet skew correction motors 68 to convey the sheet P.